Effects Of Five Aquatic Plant Extracts On The Growth Of Scenedesmus Obliquus

Aquatic plants are an indispensable part of landscape waters.They not only can play an ornamental value,but also protect the environment,purify water and maintain ecological balance.For example,if aquatic plants are planted in the water body area,the algal blooms are controlled by the characteristics of aquatic plants and algae.However,field investigation showed that algae blooms still occurred in natural waters.In order to find out the reasons,five common aquatic plants including Acorus calamus,Pontederia cordata,Nymphaea spontanea,Azolla imbricate and Potamogeton were carried out in allelopathic control experiment to study the effects of these five aquatic plant extracts on the growth of Scenedesmus obliquus and the effects of nutrients on allelopathic inhibition of S.obliquus.The main results are as follows:(1)The sensitization and algae inhibition of the five aquatic plants was affected by the plant species and the concentration of the extract.When the concentration of extracts of Calamus and Pontederia cordata is less than 1.0 g/L,the growth of S.obliquus is promoted.When the concentration is more than 4.0 g/L,the growth of S.obliquus is inhibited.When the concentration of extract is 16.0 g/L,the maximum inhibition rate were 75.4% and 66.1%,respectively.When the concentration of Nymphaea spontanea and Manjianghong extract was less than 4.0 g/L,the growth of S.obliquus was promoted.When it was greater than 8.0 g/L,the growth of S.obliquus was inhibited and the maximum inhibition rate were 68.3% and 53.4%,respectively.When the concentration of submerged plant valerian extract was more than 1.0 g/L,the growth of S.obliquus was inhibited and inhibition rate was higher than 40.5%.(2)Five aquatic plant extracts induced the formation of the population of S.obliquus.On the fourth day of cultivation,a population of S.obliquus appeared.With the concentration of extract of Acorus calamus and Pontederia cordata from 4.0 g/L to 16.0 g/L,the proportion of S.obliquus population increased 34%-94% and 31%-93%,respectively.With Nymphaea spontanea and Manjianghong concentration of extract was increased from 4.0g/L to 16.0g/L,the proportion of S.obliquus population increased 53%-96% and 53%-95%,respectively.With the concentration of extract with Valeriana was increased from 4.0g/L to 16.0 g/L,the population distribution ratio of S.obliquus increased 38%-94%.(3)Under the different levels of nitrogen and phosphorus nutrition,the concentration of A.glabra extracts was different for the growth of S.obliquus.Under the medium nutrient level(TN: 1mg/L,TP: 0.1mg/L),the growth of A.glabrata was inhibited when the concentration of A.glabra extract was 4.0,8.0,12.0,16.0g/L,and the inhibition rate was 24.5%.56.3%,67.1%,77.1%;eutrophication level(TN: 2mg/L,TP: 0.2mg/L),inhibition of oblique grid when the concentration of calamus extract is 4,8,12,16g/L,the inhibition rate of algae growth was 23.7%,54.4%,65.4%,and 75.4%,respectively.The inhibition rate increased with the concentration of A.calamus extract from 4.0g/L to 16.0g/L.Under the condition of super eutrophication(TN: 5mg/L,TP: 0.5mg/L),the concentration of A.calamus extract had no significant effect on the growth of S.obliquus.(4)When the concentration of five aquatic plants was 1.0g/L,the effect on the standard diameter and malondialdehyde content of S.obliquus cells was small.When the concentration of the extract is increased to 4.0 g/L,malondialdehyde accumulates in the algal cells,the algae cell membrane is destroyed,and the standard diameter of the algae cells increases,which may be the cause of the cell death caused by allelochemicals.In order to resist the stress of allelochemicals,S.obliquus increases extracellular polysaccharides,forms extracellular rubber sheaths,promotes the formation of algae cells,and maintains the growth of algae cells.(5)The medium nutrient level has small cell density,cell standard diameter growth,malondialdehyde content and EPS content,which is conducive to the formation of the population,the increase of nitrogen and phosphorus nutrient levels,and the allelopathic substance in the iris extract.The stress of the phytoplankton cells was weakened under the same concentration of extract,the effect of different nitrogen and phosphorus nutrition levels on the growth of S.obliquus was medium nutrient> eutrophic> superrich.